Air cushion vehicle

ABSTRACT

An air cushion vehicle particularly useful for a drilling rig for oil wells and the like employed in arctic environments having open water, muskeg, ice, snow, and tundra is described. A technique is also described for preparing an artic drilling site for the air cushion supported drilling rig by flooding an area and freezing the water.

United States Patent [1 1 Blurton et a1.

E-EH 1 Oct. 29, 1974 [54] Am CUSHION VEHICLE FOREIGN PATENTS OR APPLICATIONS 1 1 lnvemorsi Blumn, BT63, Calif 1,144,201 2/1963 Germany 61/36 A Saverio J. Cina, Brooklyn, NY.

[73] AssIgnee: Marine Inc., Los Angeles, Primary Examiner jacob Shapiro Attorney, Agent, or Firm-Christie, Parker & Hale [22] Filed: May 24, 1973 [21] Appl. No.: 363,524 M Related US. Application Data [57] ABSTRACT [62] Division of Ser. No. 130,462, April 1, 1971, which is a division of Ser. No. 12,778, Feb. 19, 1970, Pat. No. An air cushion vehicle particularly useful for a drilling rig for oil wells and the like employed in arctic environments having open water, muskeg, ice, snow, and [52] US. Cl 61/46.5, 61/1, 62/235 tundra i d ib d A t h i ue is also described for f B63) 35/44, E02) 17/00, B6313 preparing an attic drilling site for the air cushion sup- [58] FIeld of Search 61/46.5, 46, 50, 1, 36 A; ported d illi i b fl di g an area and freezing the 1 5/ 62/235 water.

[5 6] References Cited 3 Cl 4 D F UNITED s ATEs PATENTS m 3,675,430 7/1972 Haimila 61/50 M A N m 3 PAIENTEDumze 1914 3.844126 m1 ear 4 PATENTEnnm 29 1914 3.844. 126

sum 30; 4

- llllllll AIR CUSHION VEHICLE I CROSS REFERENCE TO RELATED APPLICATIONS BACKGROUND I In recent years there has been considerable interest and exploration for oil and gas reserves in arctic regions, particularly in Alaska and northern Canada. In order to exploit these established oil and gas reserves, wells must be drilled under quite adverse conditions associated with the low temperatures of the arctic environment. Some of the areas of interest are in water in areas protected from the open sea, and these areas may be open in part of the year and frozen over in other parts of the year. In other regions, a substantially permanent layer of ice is encountered. Snow is found in some regions; and still others are what is known in the arctic as muskeg, which is a boggy marsh unable to support ordinary land vehicles. Other areas of the arctic are tundra, which are open, treeless plains, having a blanket of organic material overlying a permafrost wherein a subsurface portion is permanently frozen and the surface portionis annually thawed to produce a mucky surface soil.

In order to minimize the cost of arctic operations, it is desirable to move a completely assembled drilling unit from drilling site to drilling site. The length of time that a drilling rig is on a site is nonnally in the orderof from about days to about 6 months, with the most usual time being in the range of 2 or 3 months. Clearly, if it is necessary to disassemble and reassemble the drilling unit for transport to a new site with such frequency, a very large item of expense is involved.

When a drilling platform is provided on tundra, it is desirable to minimize the effect on the tundra. If the tundra is damaged, its inherent insulation may be destroyed and underlying permafrost may be melted. A technique is therefore desirable for preparing a drilling site to receive a platform and maintain it in a fixed position for a substantial period of time without damage to the underlying surface.

BRIEF SUMMARY OF THE INVENTION Therefore, there is provided in practice of this invention according to a preferred embodiment a technique of establishing a temporary drilling site by erecting a barrier around the site and flooding it with water. The water is then frozen and a portable drilling station placed on the resulting ice. Preferably, the drilling station is brought to the site on a cushion of air and lowered onto the surface by depleting the cushion of air.

DRAWINGS These and many other features and advantages of this invention will be appreciated as the same becomes better understood by reference to the following detailed description of a presently preferred embodiment when considered in connection with the accompanying drawings wherein:

FIG. 1 illustrates in perspective a drilling rig being transported on an air cushion vehicle constructed according to principles of this invention;

FIG. 2 is a side partial cross section of the apparatus of FIG. 1;

FIG. 3 is a top view of the apparatus of FIG. 1; and

FIG. 4 is a schematic view of a combined drilling rig and air cushion vehicle on a prepared drilling site;

DESCRIPTION FIG. 1 illustrates in perspective a combined drilling rig and air cushion vehicle constructed according to principles of this invention. As illustrated in this embodiment, a vehicle 12 is being towed by a conventional tractor 13 across an ice field or other arctic terrain. Surrounding the vehicle 12 is a flexible skirt 14 within which a large volume of air at increased pressure is pumped in order to lift the vehicle on a cushion of air trapped within the skirt. A shelter 16 on the main deck of the vehicle provides a habitable environment for workmen on the drill rig and protects drilling equipment from the severe arctic environment. A'drilling tower 17 is mounted on the vehicle for handling the lengths of drill pipe employed in the conventional drilling and completion of an oil well or the like. The tower 17 in its drilling position (not shown in FIG. 1) is erect above the vehicle in the familiar posture of oil wells. During transport, however, in order to maintain the overall center of gravity of the vehicle as low as possible, and' to lower the center of pressure of wind forces on the vehicle, the tower is folded to a lowered position. In a preferred arrangement, the tower has a lower section 18 and an upper section 19 which fold relative to each other as the lower section 18 folds down so that the transverse center of gravity of the tower is not greatly shifted between the raised and lowered positrons.

FIGS. 2 and 3 illustrate'in longitudinal cross section and top views, respectively, many of the construction details of the apparatus illustrated in perspective in FIG. 1. In both of these views the shelter 16, illustrated in FIG. 1, is removed to show elements of the equipment which would otherwise be protected and hidden by the shelter. The main body of the vehicle comprises a platform or chassis 21. In a typical embodiment, the platform is about 64 feet long and about 46 feet wide, which provides sufficient room for the equipment required for drilling and completing an oil well.

The total weight of the vehicle, including the drill rig and various expendables when set up for drilling, applies a weight of about 275 pounds per square foot which can safely be supported on a layer of ice about 5 feet thick. When the vehicle is traveling the footprint pressure is appreciably less due to decreased total weight because of the absence of expendables and a larger footprint area so that the traveling footprint pressure in about lbs per square foot (0.8 psi).

Mounted on the platform of chassis 21 is a so-called sub-base 22, which provides a raised deck for workmen during drilling operations and which supports a portion of the equipment required for drilling operations, such as, for example, the approximately centrally located rotary table 23 conventionally employed in drilling operations. Mounted on the sub-base 22 are foundations 24 on which the lower segment 18 of the tower 17 is sup- 3 ported '(the tower 17 is omitted from FIG. 3 for clary)- When the tower is folded, as illustrated in solid in FIG. 2, its overall transverse center of gravity is substantially directly below the center of gravity of the elevated tower. in this manner, the overall center of gravity of the vehicle is not greatly shifted whether the tower is in a raised or lowered position. This enables the footprint weight distribution to be predicted and controlled when the tower is raised so that the weight distribution on the surface beneath the platform is fairly uniform to prevent tilting. Likewise, the center of gravity remains substantially centrally located with the tower lowered so that the vehicle remains balanced when traveling on a cushion of air.

Diesel engines 43 can be selectively connected to a pair of high volume low-pressure blowers 47. Each of the blowers 47 is connected to an air duct 48 which leads the air through the edge of the platform which is in the form of an outwardly extending flange 49 having intermittent braces 51 for weight support.

Air from the ducts 48 enters an upper plenum 52 of the skirt 14. The plenum 52 having an edge connected to the flange 49 continues as an open passage entirely around the platform so that air entering from the two ducts 48 is conveyed within the skirt entirely around the vehicle. The lower portion of the skirt 14 includes a plurality of webs 53 lying in a substantially vertical plane and connected in one corner to the platform 21. The'outer edge of each web 53 is connected to the outer exposed portion of the skirt and the inner edge is connectedto an inner skirt 154 which extends entirely around the platform and is fastened thereto at its upper edge by a bar 56. The bottom portion of the skirt 14 is completely open adjacent the ground 57, for example, so that air can leave the skirt through the open bottom portion.

The skirt '14 is fabricated of a flexible material, and because of the low temperature environment encountered in the arctic, care must be taken in selecting a flexible material that will not harden or become brittle at low temperatures. Polyurethane impregnated fabric materials, which remain flexible at arctic temperatures, are suitable for use in the skirt.

in operation, air is injected into the plenum 52 through the ducts 48 and the upper portion of the skirt is caused to billow outwardly as illustrated in FIG. 2

under the urging of the increased air pressure. The webs 53 constrain the lower portion of the skirt and maintain it in the general configuration illustrated. Air passes downwardly from the plenum 52 through the spaces between the webs 53 which may, for example, be one or two feet apart, and escapes between the lower edges of the skirt and theground 57. A portion of the air passes under the inner skirt 54 to increase the air pressure underneaththe platform 21, and the principal portion of the air escapes beneath the outer skirt 14 into the environment. The air pressure built up within the inner skirt 54 and under the platform is substantially the same as the air pressure within the plenum 52, and as this builds up it applies a force against the bottom of the platform which serves to raise the platform to a position as illustrated in FIG. 2. When so raised, the bottom of the platform is about feet above the ground in the illustrative embodiment, and it is found that obstacles about 2 1% feet high can readily be cleared with such an arrangement.

As air is applied within the skirt 14, it does not continue indefinitely to increase pressure and further raise the platform above the ground, since as the platform raises the outer edge of the skirt will clear the ground and air will leak out around the skirt. An equilibrium clearance above the ground is quickly established with the leakage around the skirt equalling the volume of air inserted into the plenum by the blowers 47. With a vehicle of the size and weight herein described and illustrated in a preferred embodiment, the outer edge of the skirt may be as much as 3 inches from the ground surface when a full volume of air is escaping therefrom. Additional details of the air cushioned vehicle and drilling rig are set forth in the aforementioned parent application.

As illustrated in FIG. 1, the air cushion vehicle would normally be towed by a tractor; towing can also be by a second air cushion vehicle or a helicopter, if desired. Either of these latter two modes may be preferable when the vehicle is towed over water, or ice over water, since they also have low footprint pressure as compared with a tractor. in particularly steep terrain, winches 75 mounted on the deck of the platform can be employed to manipulate cables connected to objects solidly affixed to the terrain, such as trees, piling or the like.

Just as in other drilling rigs a reasonable foundation for the platform must be prepared at the drilling site. If the drilling site is in open water, the vehicle is merely moored and floats at the site. Similarly, if the drilling site is in a muskegbog, the platform is merely set on the surface of the bog and may sink some distance into the marshy ground without any problem whatsoever. On tundra, bulldozers may be employed for leveling and smoothing a site for the drilling platform, or if it is during the winter months, a technique similar to that suitable for smoothing and leveling an ice surface is preferred.

Such a technique is illustrated schematically in FIG. 4 wherein uneven ground is smoothed by erecting a cofferdam 79 surrounding the drilling site. The area within the cofferdam is then flooded with water to a sufficient depth to cover any objectionable irregularities, and the water is then frozen to form a smooth level layer of ice 81. If a production well is to be maintained on the site, it may be desired to leave a subsurface cellar 82 in the region immediately below the tower 17. This provides a location for the blow-out preventer and other production equipment which may be installed on the well prior to departure of the drilling rig. This equipment is preferably installed in the cellar 82 so that the air cushion vehicle clears the equipment when it leaves the site. The cellar can be temporarily covered so that the air cushion is not lost as the skirt traverses the cellar. If the technique is employed on ice, the blow-out preventer is normally installed on the bed of the body of water beneath the ice. Also, in employing the technique on ice, the extent of the body of ice formed within the cofferdam 79 may extend a considerable distance beyond the drilling platform in order to raise the thickness of the ice to at least 5 feet for a sufficient distance to accommodate the stresses of the heavy drilling platform without breaking through the ice.

When the drilling platform is installed on ice, whether in its original condition or made by freezing a pond as illustrated in FIG. 4, care must be taken to avoid melting the ice due tothe heat generated by the drilling rig. If the ice is melted, a problem may be encountered wherein the drilling rig freezes to the ice surface so that it cannot be readily moved to a new site. in order to avoid melting of the ice beneath the platform an insulating layer 83 is first laid over the ice prior to installing the platform in position. A suitable insulating' material having low thermal conductivity and sufficient strength to bear footprint pressures of the order herein involved is readily available commercially in large slabs, which can be laid directly on the ice and cemented together with hot asphalt or the like in order to form a continuous layer. Such arrangements are also employed in arctic airfields. Another suitable insulation involves a layer of styrofoam overlaid with 2 or 3 feet of gravel.

Rather than employing insulation over the ice there are also situations where it is desirable to provide artificial cooling to maintain the ice beneath the vehicle. Thus, as seen in the cutaway portion of FIG. 2 conventional refrigeration coils 84 are laid in good thermal contact with the bottom of the chassis 21 for cooling that surface. The coils 21 can be used for maintaining ice frozen beneath the platform and are also useful for initially forming a pad of ice to support the loaded weight of the platform when the ambient temperature is not sufficiently low to quickly freeze a sufficient layer of ice. The coils 21 can also be used for heating and deliberately thawing ice beneath the platform to prevent sticking when it is desired to move the platform to a new location.

In order to move the air cushion supported drill rig from one drilling site to another, any remaining expendables are removed from the platform in order to minimize the weight, and the drill tower is lowered. As

the blowers 47 inflate the skirt and increase the air pressure beneath the platform, a pressure is soon reached where the platform is lifted off of the surface so as to ride on a cushion of air. As soon as the vehicle is stabilized, towing to a new site can commence.

Although only one technique for placing a drill rig on a frozen drill site has many modifications and variations will be apparent to one skilled in the art. It is therefore to be understood that the invention may be practiced otherwise than as specifically described, limited only as is indicated in the appended claims.

What is claimed is:

l. A method of establishing a temporary drilling site comprising the steps of:

surrounding the drilling site with a watertight barrier;

flooding the site within the barrier with water; exposing the water to sufficiently low temperature to .freeze the water, thereby producing a substantially flat, level, solid surface; and placing a portable drilling station on the solid surface. 2. A method as defined in claim 1 wherein the step of placing comprises the steps of:

supporting a portion of the weight of the drilling station on a cushion of air; towing the drilling station so supported to a position over the solid surface; and depleting the air cushion for lowering the drill platform onto the solid surface. 3. A method as defined in claim 1 wherein the drilling site is on uneven ground wherein the flooding step comprises flooding the site within the barrier to a sufficient depth to cover irregularities.

UNITED STATES PATENT OFFICE. CERTIFICATE OFCORRECTION Patent No. 3,844,126 Dated October 29,1974

Inventor) Leon C. Blurton, Saverio J. Cina It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

,Title shouldqread -METH OD OF ESTABLISHING A DRILLING SI'IE;

Column 3, line 16, the following paragraph should be inserted: --A conventional 'pipe rack-34 is provided on the platform 21 for acceptinglengths of drill' pipe employed in drilling operations. A tank 36 for drilling mud is also provided-on the platform, and in a position approximately opposite the center of gravity from the pipe rack 34, so that substantial amounts of pipe andmud in their respective receptacles do not grossly change the over all center of gravity of the platform. Other a conventional well drilling equipment, such as, for example, pumps 37, an active mud, tank 38, pipe setbacks 39, and blow-out preventer control equipment 41 is also positioned ,on the main deck of the platform in a distribution that assures a vehicle centerof gravity near its geometrical center.-

' Column 6, line 7, -been described and illustrated herein-- should be inserted after "has" and before "many".

Attest: v

' C. I-IARSHALL Dem:

RUTH C. hl-ESON Commissioner of Patents fittest-ins, Officer I and Trademarks 

1. A method of establishing a temporary drilling site comprising the steps of: surrounding the drilling site with a watertight barrier; flooding the site within the barrier with water; exposing the water to sufficiently low temperature to freeze the water, thereby producing a substantially flat, level, solid surface; and placing a portable drilling station on the solid surface.
 2. A method as defined in claim 1 wherein the step of placing comprises the steps of: supporting a portion of the weight of the drilling station on a cushion of air; towing the drilling station so supported to a position over the solid surface; and depleting the air cushion for lowering the drill platform onto the solid surface.
 3. A method as defined in claim 1 wherein the drilling site is on uneven ground wherein the flooding step comprises flooding the site within the barrier to a sufficient depth to cover irregularities. 